that 7.5 ph soil will buffer that lemon right up to 7.5
you could side-dress with peat......a nice thick layer to water through. i think that will slowly drop your ph. or water in some sulfur.
Uh, no. please do not gues when it comes to some one elses grow.
Ph adjustment should be made using pH up or pH down (purchased at your local hydro store) along with a good quality pH meter. myron meters are the tits, hanna will do, but rapitest is bullshit.
do not use lemon juice, baking soda, vinegar, or any other cheap form of pH adjustment.
pH is critical to nutrient uptake so treat it as such.
pH the water you plan to water with, or pH your water after you add nutrients, then water. do not try to compensate for pH: i.e, if soil is 7.5 pH, dont water with 5.5 pH in soil to comensate. just use 6-6.7 pH water/nutes every time. water more than you normanll would, but dont increase frequency. example: instead of adding 1 gallon of 6.5 pH water to a 3 gallon pot, add 3-4 gallons of 6.5 water per 3 gallon pot.
if you have questions post again. If you get advice on this, or any other site, without getting at least 2-3 people to back it up, consider it useless advice from people who would rather guess than read a book.
Side note: If you have no idea what the right answer is, look it up, dont guess. have some sense of empathy and imagine it was your grow.
sorry in advance for the rant.
I hope my advice was helpful... ask others and you will see your way through this. your questiuon is not uncommon and is a good question to be asked. good luck in the future with your grow.